Reference to background art herein is not to be construed as an admission that such art constitutes common general knowledge.
In the extraction of hydrocarbon resources from beneath the earth's surface it is often necessary to overcome a low or negative pressure differential between the pressure of the hydrocarbon fluids in the reservoir pores and the hydrostatic head of that fluid in wells penetrating the reservoir from the surface. This is often achieved using a submersible pump that adds energy to a fluid to increase its flow rate and static pressure. Typical submersible pumps either employ downhole motors, such as electrical submersible pumps, or alternatively surface motors, such as reciprocating pumps and rotary progressive cavity pumps (PCP). Reciprocating and rotary pump types are activated by a rod string that is installed inside the production tubing.
In some embodiments, the pump is directly in line with the production tubing. When the pump shuts down, either planned or unplanned, fluid may flow back down the tubing and into the outflow port of the pump. This may occur until the level of fluid in the tubing equals that in the tubing annulus surrounding the tubing. In other situations, the pressure within the tube may increase, pushing fluid back down the tubing and into the pump. Whatever the cause, a reverse flow of fluid into the pump can cause mechanical damage. For example, the fluid may possibly cause spinning of the pump in reverse. The downward flow through the pump will also bring any solids entrained in the fluid back into the pump. Should this occur, the solids settle and pack in impellers and bearings and become impregnated in exposed elastomers, causing damage to the pump on later restarting, or cause the pump to seize completely if the torque required to turn the solids-laden pump exceeds the torque capacity of the drive motor. Also, at times, the tubing string or the pump can pack off or plug after a shut down. This may prevent flow back down the tubing. If the tubing does not drain, the operator may then have to bail out the production fluid before pulling the pump and tubing. Bailing involves running a bailer on a wireline repeatedly down into the tubing, taking time. This downtime can result in lost production and increased expenses for workmen and materials. Preventing solids from falling back into the pump is therefore desirable to prolong pump run life and reduce frequency of costly workovers.
One prior art approach is described in U.S. Pat. No. 6,289,990 awarded to D. B. Dillon et al, entitled “Production Tubing Shunt Valve”, which describes apparatus and methods for preventing solids from falling back into electrical submersible pumps. However, the apparatus claimed does not include a passageway for a rod string through the centre of the Production Tubing Shunt Valve needed to operate and protect the progressive cavity pumps.
Another prior art approach is described in U.S. Pat. No. 8,545,190 awarded to Lawrence Osborne, which describes a shunt valve device that can be used with progressive cavity pumps, but which does not incorporate means for disassembly of the valve to replace damaged or worn parts and thus has a limited run life. Moreover, with ready means for disassembly, typically the potential for the valve to fail during use, particularly due to the torque induced along a flow string, is increased.